The present invention relates to sealing machines for shrink wrapping and other type of packaging.
As known in the art, hand-fed and automated wrapping of items, and in particular, shrink wrapping, involves the following process. A center-folded plastic sheet wrap is pulled from its roll over a separator bar or plate to separate the wrap about the fold thereby providing a space for insertion of the product to be sealed by the wrap. The leading edge of the wrap, if not sealed together, is then sealed. If it is intended to ultimately shrink the wrap around the product with hot air, holes are made in the wrap usually by the application of hot or cold punches prior to or after pulling the wrap to the area in which the product to be packaged is inserted. The product is then inserted into the wrap, that is, between both sides of the wrap defined by the fold, and the product and wrap are then pulled to a sealing area. Here a sealer frame shaped like a reverse L is pulled down onto the wrap around the product. The sealer frame is designed to carry heat so that when it is lowered and pressed onto the wrap around the product, it seals both sides of the wrap together in the area where the sealer bar is present, thereby sealing the product in the space within the wrap. When the sealer frame touches the wrap, it softens and bonds or laminates together the two sides of the wrap both under and near the frame. If the frame is left on the wrap for an adequate period of time, the heated plastic wrap under the frame melts away from the remaining wrap so that when the reverse-L sealer frame is lifted, the product and its surrounding wrap stand independent of the remainder of the wrap and may be readily moved to the hot air shrinking area. The edge of the remaining portion of the wrap is sealed from the heat generated from the sides of the reverse-L sealer frame. Thus, when the reverse-L sealer frame is again brought down for the next product, the next product is fully sealed on all sides.
In the shrink-wrapping process, the sealed product is transferred to an area in which hot air is applied to shrink the wrap tightly around the product. The holes in the wrap formed earlier by the hot or cold punches allow the air trapped between the wrap and the product to escape so that the wrap shrinks to the size of the product contained within its bounds without an air pocket being formed therebetween. During such shrinking process, the hot or cold formed holes do not seal closed.
One disadvantage of the foregoing wrapping method is that it provides no means for removal of the product once the wrapped product has reached its ultimate consumer. The user is left to use outside cutting means to sever the wrap to release the product. At times, this can result in the user inadvertently damaging the product in the process of cutting away the wrap.
A second disadvantage is the requirement of the additional step of "venting" the wrap by punching holes therein should shrink wrapping be desired.
A third disadvantage is that the product is sealed on all four sides when it may be desired that one side be left open.
Known sealing devices are disclosed in U.S. Pat. No. 4,697,401 to Kessler, U.S. Pat. No. 3,123,955 to Weissensee, U.S. Pat. No. 4,512,138 to Greenawalt, and U.S. Pat. No. 3,681,890 to Pringle.
U.S. Pat. No. 3,681,890 to Pringle addresses the first disadvantage noted herein by disclosing a machine in which a tear tab is heat-sealed to the seam of each wrap for tearing open the wrap to get to the enclosed product. However, the tear tab disclosed by Pringle requires the addition of an extra step to the sealing process, that of attaching a tear tab. Further, the tear tab is not fail proof. If it is not properly sealed to the wrap, it may rip free of the wrap without creating an opening in the wrap to reach the inside product This is particularly likely with the Pringle method since the tear tab is attached to a seam area, one of the stronger areas of the wrap and thus one of the areas least likely to rip.
Kessler in U.S. Pat. No. 3,123,955 and Weissensee in U.S. Pat. No. 3,123,955 address the issue of maintaining one open edge of the product but do so by adding the step of cutting that edge open after the product has been sealed within the plastic wrap.
The present invention discloses a tear tab that is integral with the sealing wrap rather than merely attached to the wrap. Therefore, it is a tab that will not rip away from the wrap without ripping the wrap too. It does this without adding an additional step to the packaging process.
The invention also discloses a method of providing venting while eliminating the step of using hot and cold punches.
Finally, it discloses a means of packaging a product in a wrap while leaving one side of the wrap unsealed and therefore open to enable removal of the product. It does this without adding a cutting or other additional step to the known packaging process.